Cardiac implantable demand pacemaker



Nov. 18, 1969 w. GREATBATCH 3,478,746

CARDIAC IMPLANTABLE DEMAND PACEMAKER Filed May 12, 1965 2 Sheets-Sheet 1 Q l-0IVEIEART BEAT F! G. I

INVENTOR. WIL SON GREA TBA TCI-I A 7' TORNE).

2 Sheets-Sheet 2 Filed May 12, 1965 A 7 TOR/VEK United States Patent M 3,478,746 CARDIAC IMPLANTABLE DEMAND PACEMAKER Wilson Greatbatch, Clarence, N.Y., assignor to Medtronic, Inc., Minneapolis, Minn., a corporation of Minnesota Filed May 12, 1965, Ser. No. 455,132 Int. Cl. A61n N36 US. Cl. 128-421 4 Claims ABSTRACT OF THE DISCLOSURE A portable, self-contained, demand cardiac Pacemaker including circuitry which senses each natural heartbeat and resets the Pacemaker pulse generator timing in response to it. The Pacemaker stimulates only skipped beats and does not compete with natural beats, The first generated pulse after a natural beat occurs after a preset time interval slightly longer than the natural interval unless another natural beat has intervened. When a natural beat intervenes, the Pacemaker timer is coordinated with it.

This invention relates to electronic cardiac Pacemakers and more particularly to cardiac Pacemakers implantable within the human body which respond only to a demand from the heart, should the hearts own natural pacemaker miss a beat or fail to function.

The history of electronic cardiac pacemaking begins in 1952 when Dr. 2011 demonstrated a device capable of passing a stimulating impulse through the closed chest strong enough to elicit a heart beat. Some sick hearts, affected by complete heart block, are unable to initiate their own beat and thus cannot maintain an adequate heart rate without the aid of an auxiliary electronic stimulation of this type. Zolls stimulator was useful however only for short-term application since the current levels required were so high that stimulation was accompanied by severe pain and, after a day or so, by severe burning of the skin at the electrode site.

My invention of the implantable cardiac Pacemaker, US. Patent 3,057,356 permitted innocuous, painless, longterm cardiac stimulation at low power levels by utilizing a small, completely implanted transistorized, battery operated Pacemaker, connected via flexible electrode wires directly to the myocardium or heart muscle. This device is now a well accepted prosthetic and over 8,000 such units have been made, sold and used during the past five years.

My original invention taught a simple, fixed-rate stimulator whose rate was not automatically changed at will, in accordance witht the bodys needs. A subsequent invention of William M. Chardack, US. patent application No. 231,349, now US. Patent No. 3,198,195, issued Aug. 3, 1965, teaches variable Pacemaker controls, adjustable from outside the body by a percutaneous needle, to change Pacemaker rate and/ or output level.

In an article by D. A, Nathan, S. Center, C. Y. Wu and W. Keller, An implantable Sychronous Pacemaker for the Long-Term Correction of Complete Heart Block, American Journal of Cardiology, 111362, there is described an implantable cardiacPacemaker whose rate is dependent on the rate of the hearts natural pacemaker, picking up the heart beat signal on an auricular sensor electrode and, after suitable delay and amplification, delivering a corresponding delayed stimulus to the ven tricle to initiate each heart contraction.

These devices, separately or in combination, tend to alleviate some examples of complete heart block. However, one complication remains which can in some instances prove serious. Specifically, if the heart itself periodically competes with the artificial Pacemaker for con- 3,478,746 Patented Nov. 18, 1969 trol, occasions can arise when an electronic Pacemaker stimulus falls into the T wave portion of each complete beat, the T wave following each major beat pulse (the R wave) by about 0.3 seconds, Within the T wave is a critical interval known as the vulnerable period and, in the case of a highly abnormal heart, a Pacemaker impulse falling into this period can conceivably elicit bursts of tachylcardia or fibrillation which are undesirable and may even lead to fatal sequence of arrythmias.

An object of my invention is to provide an implantable cardiac Pacemaker which operates only upon a demand signal from the heart itself.

Another object of my invention is to provide an implantable device which senses any arrest of normal cardiac activity and subsequently delivers timed electrical pulses to the heart in such a way as to restore a more normal cardiac rhythm.

Still another object of my invention is to provide an an implantable cardiac Pacemaker whose activity is govfrom its battery supply is greatly reduced during times of normal cardiac activity when auxiliary stimulation from the Pacemaker is not needed.

Still a further object of my invention is to provide an implantable cardiac Pacemaker whose activity is giverned by sensory impulses received over the same electrodes over which a stimulation impulse may later be supplied, so that no extra electrodes are needed for the sensory function.

Yet another object of my invention is to deliver stimulation impulses to the heart in such a manner that the first pacemaker stimulus follows the last previous natural beat by a pre-set time interval, approximately equal to the designed period of the implanted artificial Pacemaker,

My invention provides an electronic demand Pacemaker, implantable within the human body which is inhibited during normal cardiac rhythm and activated only upon demand of the heart, that is to say, when it misses a beat or fails to function.

Very importantly, I provide a small, low-powered, transistorized circuit with a self-contained mercury battery power supply (or other suitable supply including rechargeable batteries), all encapsulated in a moisture-proof and reaction-free enclosure so as to permit long-term implantation within the human body. This feature in combination with my novel circuitry permits a result not heretofore attainable, namely the excitation, upon demand, of an ailing heart, without the necessity of transcutaneous wires, battery chargers or any other extracorporeal device of any kind.

According to my invention, there is provided an implantable demand cardiac Pacemaker including a semiconductor pulse generator, a moisture-proof human body reaction-free enclosure enveloping the Pacemaker, a plurality of electrodes coupled to the pulse generator at least one of which is adapted to contact a heart and means coupled to at least one of the electrodes and responsive to the natural beat of the heart for inhibiting a pulse normally generated upon the electrodes whenever itis preceded by its corresponding natural beat of the heart.

In one particularily advantageous embodiment of the invention, the implantable demand cardiac Pacemaker provides the first generated beat upon the electrodes at a predetermined time interval from the natural heartbeat.

Other objects and features of the present invention will be set forth or apparent in the following description and claims and illustrated in the accompanying drawings, which disclose by way of example and not by way of limitation, in a limited number of embodiments, the principle of the invention and structural implementations of the inventive concept.

In the drawings, in which like reference numbers desig nate like components in the several views:

FIG. 1 illustrates the voltage wave produced by a human heart during one complete heart beat;

FIG. 2 is a schematic diagram illustrating one embodiment of an implantable electronic demand Pacemaker according to the invention;

FIG. 3 is a schematic diagram of a modification of a portion of FIG. 2 for employing an additional electrode according to the invention;

FIG. 4 is an elevation view of one embodiment of an implantable electronic demand Pacemaker according to FIG. 2 which employs bipolar myocardial electrodes;

FIG. 5 is an elevation view of another embodiment of the invention employing the modified circuitry of FIG. 3 and using bipolar myocardial electrodes and a separate indifferent electrode;

FIG. 6 is an elevation view of a modification of FIG. 4 wherein a bipolar catheter with spaced electrodes replaces the two cables of FIG. 4;

FIG. 7 is an elevation view of a modification of FIG. 5 wherein the two cables of FIG. 4 are replaced with a bipolar catheter having two spaced electrodes; and

FIG. 8 is an elevation view of a modification of FIGS. 4, 5 and 7 wherein a plate electrode substitutes for one of the electrodes.

The human heart beat is a complex wave over the peri- 0d of each beat and it recognizably consists of P, Q, R, S and T waves all as shown in FIG. 1. The major and most pronounced pulse is the R wave and is normally of a magnitude between 2 to 10 millivolts in the ventricle, the T wave normally following the R wave by approximately 0.3 second.

A Pacemaker similar to my US. Patent No. 3,057,356 is illustrated in the top portion of FIG. 2 for providing periodic electronic pulses to the heart to supply a missing R wave. As mentioned hereinabove, if the heart also supplies a R Wave, it competes with the electronic Pacemaker pulse for control of the heart and a potentially dangerous situation arises when the Pacemaker electronic pulse occurs in a T wave region.

Referring to the demand Pacemaker as shown in FIG. 2, the upper portion thereof illustrates a free-running electronic Pacemaker, similar to one shown in US. Patent No. 3,057,356, which produces regular periodic pulses of approximately 1 pulse per second upon electrodes 10 and 12 which are surgically placed in contact with the heart of a patient. In FIG. 2, electrodes 10 and 12 are connected by wire 14 and 16 to one side of a resistor 17 and a lead 19, respectively, the wires 14 and 16 being enveloped by a moisture-proof and human body reaction-free material such as silicone rubber or suitable plastic. The other side of resistor 17 is connected through a capacitor 18 to a collector electrode 20 of a transistor 22 and to lead 19 through a resistor 24, lead 19 being connected to the positive side of a battery 26 and emitter electrode 30 of transistor 22 and the negative side of battery 26 are grounded. A capacitor 27 is shunted across battery 26 reducing the peak current drain on the battery and thereby increasing its life.

Transistor 22 provides a power amplification stage for an oscillator transistor 32 which operates in a blocking mode to provide Pacemaker electronic pulses for electrodes 10, 12 after amplification by transistor 22. A collector electrode 34 of transistor 32 is connected by a lead 36 to one side of primary winding 38 of a feedback transformer 40. The other side of primary winding 38 is connected to lead 19. One side of the secondary winding 42 of transformer 40 is connected to the positive side of battery 26 through a capacitor 44 in series with a resistor 46, the latter constituting an R-C circuit to control the timing and frequency of the generated Pacemaker pulses. The other side of secondary winding 42 is connected to a base electrode 21 of amplifying transistor 22 by a lead 48. An emitter electrode 50 is connected to ground through a resistor 52, the negative side of battery 26 also being grounded. Transistor 32 will oscillate when its base electrode 54 is connected to the junction of resistor 46 and capacitor 44 in the R-C circuit.

When no natural cardiac activity is present, the Pacemaker portion described immediately above is free running at its designed rate, which may be perhaps one pulse per second. During operation of this type, a saw-tooth voltage waveform exists at the base 54 of the oscillator transistor 32 which falls quickly to zero volts immediately upon cessation of the 2 millisecond Pacemaker pulse and then rises exponentially to 0.6 volt in about one second, driving 32 into conduction and initiating another Pacemaker pulse. If, for any reason, the base 54 of 32 is held at a voltage of less than 0.6 volt, the Pacemaker will not operate or generate pulses on electrodes 10, 12. When transistors 32 and 22 are activated to provide output pulses for electrodes 10, 12, capacitor 27 acts as an energy accumulator which is charged slowly by battery 26 in the time period between pulses generated by 32, the pulsed saturation of transistor 22 rapidly discharging capacitor 27 over a very short interval to provide large amplitude peak pulse currents for electrodes 10, 12 through capacitor 18. Capacitor 18 acts as a charging capacitor which charges in one polarity sense by the Pacemaker pulses and discharges between Pacemaker pulses to provide a reversed current. It is believed that such reversal of current through the patients heart is beneficial in that it prevents the plating of any metal upon the patients heart which may be the case if only unidirectional current was passed therethrough.

The lower portion of FIG. 2 constitutes an R wave amplifier which responds to the natural R voltage wave, when present, of a normal heart beat to inhibit, or disable, the Pacemaker circuitry above detailed so as to prevent the occurrence of generated Pacemaker electronic pulses upon electrodes 10, 12 when the heat is functioning normally.

Between generated Pacemaker pulses, a natural heart beat, if it occurred, would generate an R wave of 5 to 20 millivolts which would be conducted back over the electrodes 10, 12 and wires 14, 16 to the circuitry in the lower portion of FIG. 2. Specifically, one side of a capacitor 60 is connected to wire 14 while its other side is connected to an emitter electrode 62 of a transistor 64 by a lead 66. Also, the emitter electrode 62 is connected to the positive side of battery 26 through a resistor 67. Base electrode 68 of transistor 64 is connected by a lead 70 to a positive bias tap of battery 26 (which may preferably be at half maximum voltage of the battery. Collector electrode 72 of transistor 64 is connected to a base electrode 74 of a transistor 76 by a lead 78, the latter being connected to ground through a resistor 80. Emitter 82 of transistor 76 is also connected to ground through a resistor 84 shunted by a capacitor 86. Collector 88 of transistor 76 is connected to the high-voltage side of battery 26 through a resistor 90. Collector 88 of transistor 76 is also connected to the base electrode 92 of a transistor 94 through a capacitor 96 while a resistor 97 is connected between base 92 and emitter 99, the latter being connected to the high side of battery 26. Collector 98 of transistor 94 is connected to ground through a resistor 100 and to a base electrode 102 of a transistor 104. Emitter 106 of transistor 104 is grounded while its collector electrode 108 is connected to the base electrode 54 of oscillator transistor 32 by a lead 110. Transistors 64 and 76, together with associated circuitry, operate to amplify the R voltage signal appearing on electrodes 10, 12 as produced by a normal heart beat. Transistors 94 and 104 are switching transistors for selectively disabling or inhibiting oscillator transistor 32 whenever a natural R wave appears in the normal heart. That is to say, the natural and normal R wave will be amplified by the grounded-base transistor 64, again by the grounded-emitter transistor 76 to an adequate amplitude so that the complementary transistor switch 94, which is normally cut off, would be driven into conduction for about 20 milliseconds for delivering a saturation pulse to switch transistor 104. Transistor 104, acting as an on-oif switch, provides a low-impedance path between its collector 108 and its emitter 106 when saturated (emitter 106 being grounded). This grounds the base electrode 54 of oscillator transistor 32 long enough to discharge capacitor 44 and thereby re-initiate the Pacemaker pulse generating cycle. That is to say, switching transistor 104 by discharging capacitor 44 prevents the voltage on base electrode 54 of oscillator transistor 32 from reaching 0.6 volt, such voltage level being required to generate Pacemaker pulses upon electrodes 10, 12. Thus the Pacemaker cannot fire until about one second (the normal frequency rate of transistor 32 and associated circuitry) following the last previous natural heart beat. If the natural heart rate is faster than once per second, the Pacemaker will never fire. If the natural heat rate is slightly faster than once per second, but skips just one heat, the Pacemaker will inject only that one skipped beat. Accordingly, this invention provides a Pacemaker which generates pulses only as needed by a skipped single beat or a skipped plurality of beats. I

A modification of that portion of FIG. 2 enclosed by a (dash-dot) line indicated as M is shown in FIG. 3. In addition to the two output electrodes 10, 12 of FIG. 2, the embodiment shown in FIG. 3 employs an additional electrode 120 connected to one side of capacitor 60 by a wire 122. Such additional terminal 120 can be surgically placed in contact with a selective portion of the patients heart. Alternatively, such additional electrode 120 (commonly called an indifferent electrode) can be attached to some other portion of the patients body such as his skin. Optionally, the resistor 17 can be omitted between capacitor 18 and electrode 10.

In some cases, the invention according to the modification of FIG. 3 provides an R wave of greater magnitude.

An important feature of the invention is to permit the entire Pacemaker to be implanted within the human body. Accordingly, the entire Pacemaker, including its battery 26, is encased in an envelope 130 of a moisture-proof and human body reaction-free material such as silicone rubber or suitable plastic. Such same material is also employed to envelope the wires 14, 16 (and 122 in the case of FIG. 3) extending between the Pacemaker and the electrodes.

Physical arrangements of the Pacemaker, the electrodes and the encapsulated wires therebetween are shown in FIGS. 4, 5, 6, 7 and 8. Such physical arrangements advantageously permit the positioning of the Pacemaker between the rib-cage and the patients skin. The embodiments according to FIGS. 4 and 6 can be employed in connection with the circuitry of FIG. 2 while the em- 7 bodiments of FIGS. 5, 7 and 8 are useful in connection with the modification shown in FIG. 3.

FIG. 4 shows a typical structure of my invention employing the circuitry of FIG. 2 wherein bipolar myocardial electrodes, 10 and 12 are used for sensing cardiac activity and also for delivery of a ventricle stimulus.

FIG. 5 shows a typical structure of my invention employing modified circuitry of FIG. 3 wherein a separate indifferent electrode 120 is used to sense the diiferential voltage developed by the heart between a point on the myocardium and a subcutaneous site near the pacemaker.

FIG. 6 shows a typical structure of my invention employing the circuitry of FIG. 2 wherein a bipolar catheter 132 envelopes common intracavitary bipolar electrode wires to spaced electrodes 10, 12 for sensing cardiac activity and also for delivering a ventricular stimulus.

FIG. 7 shows a typical structure of my invention employing the modified circuitry of FIG. 3 and having a bipolar catheter 132 together with a separate indifferent electrode to sense the difierential voltage developed by the heart between an intracavitary point in the heart and a subcutaneous site near the pacemaker.

It is to be understood that electrode 12 in FIGS. 2 and 3 need not be placed in contact with the patients heart (in the manner of electrode 10) but can be contacted with other parts of the patients body. Also, that electrode 12 and cable lead 16 may be connected to ground as in my US. Patent No. 3,057,356 instead of to the positive side of battery 26 as shown in FIG. 2.

FIG. 8 shows a modification of the embodiments of FIGS. 4, 5 and 7 wherein a stainless steel or noble metal plate 121 exposed on the side of the Pacemaker is substituted for electrode 12 in FIG. 4 or indifferent electrode 120 in FIGS. 5 and 7. Accordingly, when such Pacemaker is positioned between the ribcage and the patients skin, the plate 121 can contact the interior surface of the skin.

The transistors shown in FIG. 2 may be either silicon transistors, germanium transistors, field eifect transistors, signal control rectifiers, PNPN switches or other suitable solid state devices.

While there has been described and pointed out the fundamental novel features of the invention as applied to preferred embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated and its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

I claim:

1. A portable, self-contained, demand cardiac Pacemaker comprising:

pulse generating means including timing means controlling the generation of pulses;

a plurality of electrodes coupled to the pulse generating means, at least one of the electrodes being adapted to contact a patients heart;

signal responsive means coupled to at least one of the electrodes and automatically responsive to a natural R Wave signal of either polarity generated by the heart;

the signal responsive means being operatively connected to the timing means and including means for resetting the timing means to a predetermined level in response to each natural heartbeat; and

portable, self-contained power supply means providing the sole source of power for the pulse generating means and the signal responsive means and operatively connected thereto.

2. A demand cardiac Pacemaker according to claim 1 wherein the signal responsive means is also automatically responsibe to a Pacemaker stimulated signal in the heart and resets the timing means to the predetermined level in response to a Pacemaker stimulated signal in the heart so that successive Pacemaker stimulating impulses are separated by a time interval slightly longer than that between the last natural heartbeat and the first stimulating impulse.

3. A demand cardiac Pacemaker comprising:

electrode means for connection to a patient;

electrical pulse generating means operative to selectively supply heart stimulating pulses to the electrode means; and

sensing means, operatively connected to the electrode means and to the pulse generating means and automatically responsive to the heart stimulating pulses and natural heartbeat signals of either electrical polarity, and including means for controlling the pulse generating means to supply heart stimulating pulses each separated from the preceding pulse by a predetermined time interval unless a natural heartbeat intervenes before the end of the interval and to 7 coordinate the generation of subsequent pulses With the last intervening natural heartbeat.

4. An implantable demand cardiac Pacemaker according to claim 3 wherein there are only tWo electrodes, both of which are coupled to both the pulse generating means and the sensing means.

References Cited UNITED STATES PATENTS 3,345,990 10/1967 Berkovits 128419 3,241,556 3/1966 Zacouto 128419 3,253,595 5/1966 Murphy et al. 128419 3,253,596 5/1966 Keller 128419 8 FOREIGN PATENTS 826,766 1/1960 Great Britain.

OTHER REFERENCES 5 Chardact et al., Surgery, vol. 48, No. 4 October 1960,

Davies, Journal of British Institute of Radio Engineers, vol. 24, No. 6, December 1962, pp. 453-456.

Zucher et al., Journal of American Medical Associa- 10 tion, vol. 184, No. 7, May 18, 1963, pp. 549-552.

WILLIAM E. KAMM, Primary Examiner 

